Rotary actuator with shortest force path configuration

Abstract

A parallel eccentric electro-mechanical actuator provides motive power and includes an electric prime mover that drives the reducer's pinion gear. This pinion drives minimum three star gears with stationary shaft bearings. Each shaft contains an eccentric which are completely in parallel with each other. These eccentrics can be thought of as parallel/in-phase driven crankshafts. Each eccentric drives the parallel eccentric (PE) gear through a bearing. The PE gear exhibits a circular motion (without rotation) which in itself is unbalanced. The crankshafts have another eccentric which create an opposite inertia force to balance that of the PE gear. The PE gear contains an external toothed gear on its periphery. It meshes with the internal teeth of the output ring gear. The relative motion between the PE gear and the ring gear is that the PE gear rolls inside the ring gear. This relative motion is called hypo-cycloidal motion.

What is claimed is: 
     
       1. A rotary actuator, comprising:
 an output attachment plate which rotates about a central axis; 
 an outer attachment shell; and 
 a principal bearing having a first surface which is attached to said output attachment plate, and a second surface which is attached to said outer attachment shell; wherein said output attachment plate has a first major surface, wherein said output attachment plate, said outer attachment shell and said principal bearing are arranged such that a first line exists which is perpendicular to said first major surface of said output attachment plate and which passes through said output attachment plate, said principal bearing and said outer attachment shell, and wherein said first line is parallel to said central axis. 
 
     
     
       2. The rotary actuator of  claim 1 , wherein said first line passes through said output attachment plate, said principal bearing and said outer attachment shell, in that order. 
     
     
       3. The rotary actuator of  claim 1 , wherein said principal bearing is a crossed roller bearing. 
     
     
       4. The rotary actuator of  claim 1 , wherein said output plate is axially symmetric about said central axis. 
     
     
       5. The rotary actuator of  claim 4 , wherein said outer attachment shell is axially symmetric about said central axis. 
     
     
       6. The rotary actuator of  claim 5 , wherein said principal bearing has rotational symmetry about said central axis. 
     
     
       7. The rotary actuator of  claim 1 , wherein said output attachment plate, said outer attachment shell and said principal bearing are arranged such that a first cylinder exists which passes through said output attachment plate, said principal bearing and said outer attachment shell. 
     
     
       8. The rotary actuator of  claim 7 , wherein said first cylinder is a right cylinder. 
     
     
       9. The rotary actuator of  claim 8 , wherein said first cylinder has an axis which is perpendicular to said output attachment plate. 
     
     
       10. The rotary actuator of  claim 9 , wherein said output attachment plate has a first major surface, and wherein a locus formed by an intersection of said first cylinder and said first major surface of said output attachment plate is a first circle. 
     
     
       11. The rotary actuator of  claim 10 , wherein said first major surface is a second circle, and wherein said first and second circles are concentric. 
     
     
       12. The rotary actuator of  claim 11 , wherein said first major surface is an exterior surface. 
     
     
       13. The rotary actuator of  claim 10 , wherein said output plate rotates about a central axis, and wherein said output plate is axially symmetric about said central axis. 
     
     
       14. The rotary actuator of  claim 13 , wherein said outer attachment shell is axially symmetric about said central axis. 
     
     
       15. The rotary actuator of  claim 14 , wherein said principal bearing has rotational symmetry about said central axis. 
     
     
       16. The rotary actuator of  claim 1 , wherein said output attachment plate contains a first annulus, wherein said outer attachment shell contains a second annulus, and wherein said principal bearing contains a third annulus, and wherein said output attachment plate, said outer attachment shell and said principal bearing are arranged such that said first, second and third annuli are concentric. 
     
     
       17. The rotary actuator of  claim 16 , wherein a cylinder exists whose surface intersects and is concentric with said first, second and third annuli. 
     
     
       18. The rotary actuator of  claim 17 , wherein said cylinder is a right cylinder. 
     
     
       19. The rotary actuator of  claim 16 , wherein said output plate rotates about a central axis, and wherein said output plate is axially symmetric about said central axis. 
     
     
       20. The rotary actuator of  claim 19 , wherein said outer attachment shell is axially symmetric about said central axis. 
     
     
       21. The rotary actuator of  claim 20 , wherein said principal bearing has rotational symmetry about said central axis. 
     
     
       22. The rotary actuator of  claim 1 , wherein said output attachment plate, said outer attachment shell and said principal bearing are arranged such that a force applied in a first direction normal to said output attachment plate is transmitted through said principal bearing and said outer attachment shell with essentially no transmission of force in a direction orthogonal to said first direction. 
     
     
       23. The rotary actuator of  claim 1 , wherein said outer attachment plate and said outer attachment shell are rigid in a direction orthogonal to a major surface of said outer attachment plate. 
     
     
       24. The rotary actuator of  claim 1 , wherein said outer attachment plate and said outer attachment shell are rigid in a direction orthogonal to a major external surface of said outer attachment plate. 
     
     
       25. A machine joint which includes the rotary actuator of  claim 1 . 
     
     
       26. A rotary actuator, comprising:
 an output attachment plate; 
 an outer attachment shell; and 
 a principal bearing having a first surface which is attached to said output attachment plate, and a second surface which is attached to said outer attachment shell; wherein said output attachment plate, said outer attachment shell and said principal bearing are arranged such that a force applied in a first direction normal to said output attachment plate is transmitted through said principal bearing and said outer attachment shell with essentially no transmission of force in a direction orthogonal to said first direction. 
 
     
     
       27. A rotary actuator, comprising:
 an output attachment plate; 
 an outer attachment shell; and 
 a principal bearing having a first surface which is attached to said output attachment plate, and a second surface which is attached to said outer attachment shell; wherein said outer attachment plate and said outer attachment shell are rigid in a direction orthogonal to a major surface of said outer attachment plate.